The invention relates to a throttle-valve actuator for a motor-vehicle engine, which has a servomotor to be supplied with electrical energy and, spatially separate from the latter, a potentiometer for determining the position of a shaft of the throttle valve.
Throttle-valve actuators of the abovementioned type are fitted to modern motor vehicles with so-called electronic accelerators and are therefore known. With these, adjustment of the power output is no longer effected by means of a mechanical link between the accelerator pedal and the throttle valve but by means of electrical actuating commands as a function of the position of the accelerator pedal. Here, a wiring harness leads into the throttle-valve actuator to connect the potentiometer to the actuating electronics and to connect the servomotor to electrical energy controlled by the actuating electronics. The problem with such electrical connections by means of cables is that breaks in the cables can occur relatively easily owing to vibration build-up in natural resonance. Often, there is also the risk, during assembly, that cables will be trapped between a housing and a cover to be placed on the latter. In the case of plug connections within devices, contact fretting (frictional oxidation) occurs due to movements in the area of the electrical connections and due to the effects of temperature.
The problem underlying the invention is to design a throttle-valve actuator of the type stated at the outset in such a way that its required electrical connections are as simple as possible but as insensitive as possible to vibration and to the high temperatures that occur in a motor vehicle.
According to the invention, this problem is solved by virtue of the fact that the throttle-valve actuator has a conductor bridge, which is supported firmly in the throttle-valve actuator by supports and has two rigid conductor bars for supplying energy to the servomotor and conductors for making contact with conductor tracks of the potentiometer, and that the two conductor bars and the conductors are each connected to a plug pin of a plug socket of the conductor bridge.
By virtue of this conductor bridge according to the invention, which is supported in the throttle-valve actuator, the power is distributed via a rigid component which has no tendency for vibration and with which no forces are introduced into the electrical connections to the potentiometer and the servomotor when plugging in or unplugging the plug for connection to the actuating electronics. Moreover, the conductor bridge makes it unnecessary to lay individual cables in the throttle-valve actuator and to make individual electrical connections. As a result, there is less effort involved in assembly and the space required for such cables can be saved. Moreover, the invention ensures that it is impossible for electric leads to be trapped when placing a cover on the housing of the throttle-valve actuator. The conductor bridge according to the invention could even be used as a support for additional components, e.g. for an interference suppression coil, bleed resistors, carbon motor brushes with pigtail leads and the like. A predetermined breaking point provided in the plastic could be used to allow tolerances to be compensated for by breaking off the conductor track sections that would then be exposed.
The configuration of the conductor bridge is particularly simple in terms of design if the conductor bars connect two plastic bodies, which are produced by injection moulding in an injection mould and each have one of the supports.
The conductor bridge can be produced with its two plastic bodies in a single operation by injection moulding if, according to another development of the invention, the conductor bars together with the conductors and the plug pins are designed as an insert that can be inserted into an injection mould and can there be encapsulated to give the plastic bodies at the ends.
The insert can be designed as a single one-piece component for insertion into the injection mould if in the region of the plastic bodies it has between the conductor bars and the conductors connecting webs that can be removed after injection moulding by means of punch cuts.
Contact corrosion due to relative motion between the connecting lugs of the contact bridge and the conductor tracks of the potentiometer can be completely eliminated if the conductors are seated by means of flexible connecting lugs on the conductor tracks of the potentiometer and are connected to these by a respective laser weld.
Electrical conductors can be protected very effectively from corrosion and have a high electrical conduction capacity if they are covered with a high-gloss layer of metal, in particular if they are gold- or silver-plated. However, such coatings have a high reflectivity, necessitating a high power for laser welding. However, this has the disadvantage that holes can very easily be formed by the laser beam in the material to be welded, resulting in failure to form a welded joint. Difficulties in laser welding due to excessive reflectivity can be avoided, even if the insert is completely covered with an electrically conductive high-gloss layer of metal, if the connecting lugs have a rough surface produced by stamping in the region of the laser weld. This prevents undesirably high reflection of the laser light.
The insert has a particularly good electrical conductivity and particularly low contact resistance and overall has particularly little tendency to corrosion if it is completely covered with silver.
Contact can be made with the servomotor simply by pushing on the conductor bridge without there being a risk of contact fretting if, according to another development of the invention, the conductor bars end with two contact posts in the plastic body associated with the servomotor, and the servomotor has two contact lugs, which rest at an acute angle against these contact posts and allow insulation displacement connection.
The throttle-valve actuator can also be designed in such a way that there is no need for any plug connections within its housing if the plug pins are arranged in an outer connector socket projecting in a sealed manner from the throttle-valve actuator.